It has been well known that a polyarylates composed of an aromatic dicarboxylic acid and a bisphenol are thermoplastic plastics having excellent mechanical, electrical and chemical properties, such as a high heat resistance Known processes for the production of a polyarylate include, for example, interfacial polymerization by mixing a solution of an aromatic dicarboxylic acid dihalide in an organic solvent with an alkaline aqueous solution of a bisphenol under stirring to react these materials (cf. EAREKSON J.P.S. 40 399 (1959)); solution polymerization by reacting an aromatic dicarboxylic acid dihalide with a bisphenol in the presence of a deacidifying agent such as pyridine in an organic solvent (cf. A. CONIX I.E.C. 51 147 (1959)); molten polymerization by reacting an aromatic dicarboxylic acid diphenyl ester with a bisphenol (cf. British Patent 924,607); molten polymerization by reacting an aromatic dicarboxylic acid, diphenyl carbonate and a bisphenol (cf. British Patent 1,067,314); molten polymerization by reacting an aromatic dicarboxylic acid with a bisphenol diacetate (cf. A. CONIX I.E.C. 51 147 (1959)); polymerization by reacting an aromatic dicarboxylic acid with a bisphenol diacetate in a solvent (cf. U.S. Pat. No. 4,294,956); and molten polymerization by directly reacting an aromatic dicarboxylic acid with a bisphenol (cf. JP-A-53-64298) (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
The polyarylates thus obtained have been widely employed either alone or in the form of a composition together with other resin(s) in the fields of, for example, electricity, electronics, automobiles and machinery.
However, it is frequently observed that a resin composition containing a polyarylate together with other resin(s) fails to fully exhibit the expected properties of the constituents. For example, since a composition containing a polyarylate and a polyamide excels in a chemical resistance, molding characteristics and a heat resistance, the widely use thereof in the various fields is expected, but it is disadvantageous in its low impact strength and low weld strength. That is, a composition containing a polyarylate, which may be economically produced through the above-mentioned molten polymerization (wherein an aromatic dicarboxylic acid is reacted with a bisphenol diacetate), together with a polyamide has a low impact strength and a low weld strength, similar to those obtained by other methods.
It has been proposed to solve the above problem by introducing a functional group such as an acid anhydride bond to the polyarylate. For example, U.S. Pat. No. 4,258,154 proposes a composition containing a polyarylate having an acid anhydride bond and a polyamide, to improve an impact strength and a weld strength. Further, JP-A-56-88424 discloses a process for the production of a polyarylate having acid anhydride bonds through interfacial polymerization which comprises mixing an alkaline aqueous solution of an aromatic dicarboxylic acid and a bisphenol with a solution of an aromatic dicarboxylic acid dihalide in an organic solvent under stirring. However, this process is disadvantageous since the use of the expensive aromatic dicarboxylic acid dihalide elevates the production cost. Therefore, a process is urgently required for economically producing a polyarylate capable of imparting a high impact strength as well as a high weld strength to the reaction composition produced together with a polyamide.